This invention relates to the preparation of 1,4-dicyano-1-butene by contacting a liquid phase comprising acrylonitrile with an effective amount of a polymer-bound alkyl diarylphosphinite catalyst having the formula I: ##STR2## wherein the trivalent phosphorus is substituted by one alkoxy group and one aryl group and wherein the third bond of phosphorus is a P--C bond to a pendant aryl group of the polymer matrix.
The dimerization of acrylonitrile to 1,4-dicyano-1-butene has been much investigated as a route to adiponitrile which is hydrogenated to hexamethylene diamine, the nylon 6,6 monomer.
A process for the dimerization of acrylonitrile in the presence of phosphines (PR.sub.3) and phosphites (P(OR).sub.3) to give a 2:1 mixture of 2,4-dicyano-1-butene and cis- and trans-1,4-dicyano-1-butenes is disclosed in C.A., Vol. 62 (1965), 14508e (D. W. Henberg, et al.).
Tetrahedron Letters (1966) No. 51, pp 6347-51, (W. H. Dietsche) discloses that alkyl diarylphosphinites having the formula Ar.sub.2 POR in the presence of t-butanol or aqueous acetic acid effects dimerization of acrylonitrile to 2,4-dicyano-1-butene (2-methyleneglutaronitrile) and 1,4-dicyano-1-butene.
The dimerization of acrylonitrile (ACN) in the presence of various tervalent oxygen-containing phosphorus (III) catalyst compositions and a mixture of a hydrocarbon such as toluene and a proton-donating solvent such as 2-propanol has been disclosed in a series of U.S. patents granted to personnel of Imperial Chemical Industries (ICI).
U.S. Pat. No. 4,102,915 (Jennings et al.) discloses that a process for dimerization of ACN to substantially linear C.sub.6 dimers using homogeneous, i.e., soluble organic phosphinites or phosphonites as catalysts, is effected in the presence of a proton-donating solvent and optionally a hydrocarbon co-solvent, wherein ACN and solvents are dry and free of oxygen and wherein at least one of the solvents has a boiling point higher than ACN and is capable of phase separation with respect to dimeric products, to enable unreacted ACN to be removed by distillation and the solvent(s) and dimeric products to be separated.
U.S. Pat. No. 4,316,857 (Gilbert) discloses a soluble phosphonite or phosphinite catalyzed ACN dimerization process that uses as a solvent a mixture of a proton-donating organic solvent, an aromatic hydrocarbon solvent and an aliphatic hydrocarbon solvent in a specified ratio so as to facilitate product isolation such as by phase separation or liquid extraction.
U.S. Pat. No. 4,238,422 (Cozens et al.) discloses soluble aryl phosphinites and phosphonites useful as ACN dimerization catalysts wherein the aryl groups are substituted by at least one electron-donating group.
U.S. Pat. Nos. 4,138,428 and 4,190,616 (Jennings et al.,) disclose ACN dimerization process and soluble organic phosphinite or phosphonite catalysts having at least one aryl group substituted by electron-donating substituents.
U.S. Pat. No. 4,263,224 (Jennings et al.) discloses ACN dimerization process wherein an aryl phosphonite or phosphinite is added as a low-cost scavenging reagent to a mixture of ACN and organic solvent to remove therefrom residual traces of water or other catalyst deactivating impurities before contacting said reaction mixture with a more expensive soluble aryl phosphinite or aryl phosphonite dimerization catalyst.
U.S. Pat. No. 4,126,632 (Hogan et al.) discloses a process for the dimerization of ACN to straight chain 1,4-dicyanobutenes by contacting ACN with organic phosphinite or phosphonite catalyst having the formula R.sub.1 R.sub.2 R.sub.3 P or (R.sub.1 R.sub.2 P).sub.2 R.sub.4 wherein at least one of the R groups R.sub.2 or R.sub.3 is alkoxy or cycloalkoxy and R.sub.4 is alkylene or alkylenedioxy in the presence of an inert proton-donating solvent and optionally an inert hydrocarbon co-solvent. While this patent also provides examples of soluble phosphinites and phosphonite wherein groups R.sub.1 to R.sub.4 are alkyl, aryl, cycloalkyl, polyalkylene, etc., the patent also discloses without examples that groups R.sub.1 to R.sub.4 may also be part of a polymeric backbone, for example, polystyrene or polyvinylalcohol or be linked to an inorganic support, for example, silica or alumina, so as to form a heterogeneous catalyst.
U.S. Pat. Nos. 4,059,542 and 4,089,890 (Jennings, et al.) disclose that silica- or alumina-bound phosphinites or phosphonites as heterogeneous, i.e., insoluble catalyst compositions may only be used for the gas-phase dimerization of acrylonitrile at temperatures above 150.degree. C. When the best phosphinite-bound to silica catalyst disclosed in U.S. Pat. Nos. 4,059,542 and 4,089,890 was employed for dimerization of ACN in the gas phase at 170.degree.-190.degree. C., only low conversions (7-20%) of ACN into an economically unattractive 3:1 (maximum value) mixture of straight and branched chain dimers and an unspecified amount of oligomers were observed.
The processes using soluble catalysts disclosed in these ICI patents produce 1,4-dicyanobutene, the desired linear dimer, at moderate conversions, in high selectivity with lesser amounts of the branched dimer, methyleneglutaronitrile and oligomers. However, the ACN dimerization processes employing homogeneous, i.e., soluble alkyl diarylphosphinites substituted by electron-donating groups have the following disadvantages. At the end of each ACN dimerization run, before distillation of the desired dimeric products, the soluble phosphinite catalyst must either be removed by complicated extraction procedures or decomposed with water. The extraction procedures inherently result in appreciable losses of the soluble phosphinite catalysts for two reasons. Firstly, the differences in the solubility of the soluble phosphinite catalyst in the solvents are not infinite, and thus, several extractions of the catalyst are required. Secondly, extraction enhances the chances for contamination of the solvents, unreacted ACN and catalyst with moisture and oxygen, impurities which deactivate the catalyst. Decomposition of the soluble phosphinite catalyst by the addition of water substantially increases catalyst consumption and contaminates the reaction solvents (isopropanol and toluene) and unreacted ACN with water and/or oxygen. Thus, after extraction and decomposition procedures, the reaction solvents and unreacted ACN must be degassed and redried before the recycle of same. In the case of isopropanol and ACN, degassing and redrying are very costly and time consuming steps.
One way in which the workup of the dimerization reaction could be greatly simplified, while simultaneously conserving the expensive catalyst, would be to support the catalyst on a polymer matrix. C. U. Pitman, et al. (CHEMTECH, September 1973, pp 560-566) Pitman, et al. (CHEMTECH, September 1973, pp 560-566) disclose that soluble catalysts, e.g., transition metal catalyst, may be bound to polymer backbones. See also Paper No. 29 by W. O. Haag, et al., in "Proc. 5th International Congress on Catalysis", Vol.1, pp 465-472 (1973) and an article by D. D. Whitehurst in CHEMTECH, January, 1980, pp 44-49.
During the course of development of the present invention, phosphinites bound to organic polymer matrices via P--O--C bonds were prepared and were found to be impractical and inactive catalysts for ACN dimerization. Similarly, phosphinites bound via P--O--M bonds to inorganic matrices (M), as disclosed in U.S. Pat. Nos. 4,089,890 and 4,059,542 (ICI), possess a low activity and low selectivity and may be used only for gas phase ACN dimerizations. Although the above-identified ICI U.S. patents mention the use of polystyrene-bound phosphinites, no working example of the use and/or preparation of same is given in the above-identified ICI U.S. patents or in other published literature of which we are aware.
Accordingly, it is an object of the present invention to provide an ACN dimerization process that employs a heterogeneous catalyst that avoids the complicated workup and product isolation procedures of prior art while preserving the integrity of the catalyst.
These and other objects and advantages of the present invention will become obvious in view of the following description.